The invention relates to dynamoelectric machine rotor assemblies and methods of making same, and more particularly, it relates to a segmented, laminated rim that is secured in an optimum fixed relationship to a spider by a plurality of articulated key assemblies. Pursuant to the method of the invention, a base member of each key assembly is secured by a heat-shrinking operation in axially aligned keyways formed, respectively, in the spider and the inner circumferential surface of the laminated rim.
It is common practice in the manufacture of large-diameter rotors for dynamoelectric generators to utilize locking keys between the rotor spiders and rim laminations in a manner that enables the keys to be driven with a slight force fit into aligned keyways in the spider and the rim laminations. Such a manufacturing procedure is completely acceptable for generators that are designed for rotation around a vertical axis, because any radial expansion of the rim laminations that may be caused by centrifugal forces in the rotor assembly during its operation do not cause undesirable wear or other operating problems. However, it has been discovered that when such prior art designs or manufacturing methods are employed to fabricate generator rotors that are designed to rotate around a non-vertical axis, wear-producing movement will result between the rim laminations and the rotor spider. This undesirable relative movement is due to a combination of centrifugal force and gravitational force operating on the rotor as it is spun around the non-vertical axis of the machine.
In fact, it has been found that in addition to the resultant so-called bicycle chain effect between the laminated rim and the spider on which it is mounted, further undesirable relative movement occurs in such machines between the individual rotor rim laminations. Specifically, this second type of movement involves sliding or skewing of the segmented rim laminations relative to one another due to the typically loose tolerances allowed in prior art rotor keying arrangements. Because of such loose tolerances and the types of key structures employed heretofore, each rim lamination segment is not held in direct contact with a key to prevent it from sliding or skewing relative to other rim laminations.
A typical prior art procedure used to avoid skewing between adjacent rim laminations of segmented rotor assemblies of a kind normally fabricated on-site, requires the performance of relatively expensive machining operations by which the irregular sidewalls of keyways in the rim laminations are smoothed to within close tolerances of the width of associated keys. Accordingly, when the keys are positioned in the keyways they closely abut essentially all of the laminations and prevent relative movement between them. Of course, such machining operations make it necessary to provide a large vertically reciprocable planning tool at the often-remote sites where such relatively large diameter, segmented rim assemblies are normally fabricated, thus creating an undesirably high manufacturing cost that should preferably be avoided if possible.
It is also known in the prior art to manufacture relatively small-diameter dynamoelectric generators by heat-shrinking rotor laminations directly onto a shaft to secure them and prevent the above-mentioned looping or bicycle chain effect caused by centrifugal and gravitational forces brought to bear on the laminations when the rotors are turned at high speeds. As stated above though, it has been found that if the same type of heat shrinking fabrication methods are applied to make a large-diameter rotor of the type commonly useful for non-vertical shaft hydraulic turbine generators, it is necessary to provide an undesirably heavy and expensive spider structure to support the resultant high radial compressive forces necessarily created by such typically large magnitude heat shrinking processes on the laminated rim to assure its fixed relationship with the spider when the rotor is turned on its non-vertical axis. To the extent that the number of spokes in such a spider can be reduced, the resulting cost of manufacture of the generator can be minimized, thus, it is advantageous to employ a method for securing segmented rim laminations to relatively large-diameter spiders of non-vertical shaft generators by some other means than the conventional heat-shrinking processes currently employed in making smaller diameter, horizontally mounted dynamoelectric generators.
In terms of generator size, it should be understood that the present invention is particularly applicable to relatively large-diameter generator rotors such as those having diameters in excess of twenty feet. Such relatively large-diameter rotor structures normally employ radial spokes in the spider to minimize the overall weight and cost of manufacture of the rotor assembly, as distinguished from smaller diameter dynamoelectric generators that typically have a solid rotor core. The present invention enables the use of such a relatively lightly spoked, large-diameter rotor assembly while overcoming the aforementioned disadvantages of centrifugal and gravitational forces loosening the rim laminations, or skewing them relative to one another during normal rotation of the rotor around a non-vertical axis.